1. Field of the Invention
The present invention relates to photographic developer compositions for obtaining high contrast images. More particularly, the present invention relates to photographic developers having an accelerated developing speed.
2. Description of the Prior Art
Usually, high contrast photographic sensitive materials are used in the graphic arts fields in order to photographically produce line images and halftone images. For example, line images can be formed by exposing a litho-type photographic sensitive material to an original having a continuous gradation through a screen and developing using a so-called infectious developer (Photographic Processing Chemistry, pages 163 - 165, (1966) written by Mason, published by Focal Press Library).
Since this developer has a low initial developing speed, increasing the developing speed is an obstacle. Particularly, the initial developing speed of this developer is decreased markedly if an improvement in a substantial defect of the developer (namely, low storage stability) is attempted. For example, it is known to add amines to the developer as a means for improving the storage stability (as disclosed in British Pat. Specification No. 1,192,075), but, the quality of the halftone image is further deteriorated and the initial developing speed is further decreased.
On the other hand, the addition of many kinds of development accelerators to silver halide emulsion layers has been suggested in order to increase the developing speed (as disclosed in British Pat. No. 1,098,748 and U.S. Pat. No. 3,518,085). However, it is difficult to obtain excellent halftone images. Further, if these development accelerators are added to the developer, the quality of the halftone image deteriorates because infectious development is destroyed or at least severely reduced.
As described above, prior developers for obtaining high contrast images can not provide both increased initial developing speed and excellent halftone image quality.
Accordingly, an object of the present invention is to increase the initial developing speed, that is, to provide developers which have high sensitivity in a short developing period.
A second object of the present invention is to provide developers which form halftone images having excellent quality.
A third object of the present invention is to provide developers having excellent storage stability.